1. Field of the Invention
The present invention relates to an illumination light receiver and an illumination light communications system that communicate a data signal by use of illumination light (visible light).
2. Description of Related Art
FIG. 2 is a schematic diagram showing one conventional example of an illumination light communications system. In the illumination light communications system of this conventional example, an illumination light transmitter 200 controls driving of a white light emitting device (e.g., a group of light emitting diodes that emit red, green, and blue lights, respectively) based on a data signal D inputted through a modulator 100, thereby generates illumination light X on which the data signal D is superimposed (white light modulated based on the data signal D), and shines it on an illumination light receiver 300. The illumination light receiver 300 includes a light receiving section 310 (a light receiving chip) provided with filters (see the hatched portion in FIG. 2) that allow different wavelength components (in this example, red, green, blue light components) contained in the illumination light X to selectively pass therethrough. The illumination light receiver 300 receives, for each wavelength component, the illumination light X having the data signal D superimposed thereon and then converts it into an electrical signal. The electrical signal thus obtained is demodulated into the original data signal D by a demodulator 400.
As examples of the conventional technology related to the foregoing, JP-A-2008-92303 and JP-A-2000-253211 can be cited.
Certainly, with the conventional illumination light communications system described above, it is possible to communicate a data signal D by use of, for example, visible light for indoor lighting.
However, in the conventional illumination light communications system described above, on the light receiving section 310 of the illumination light receiver 300, the illumination light with all its wavelength components is shone simultaneously. Accordingly, to receive the different wavelength components contained in the illumination light X separately, it is inevitable to form, in the light receiving section 310, filters that allow the different components to selectively pass therethrough.
These filters are typically formed of resin and therefore have the disadvantage of being weak to an external mechanical force; a scratch on the surface of a light receiving device used in the light receiving section 310 may cause a defect in characteristics. Moreover, the process of fabricating the light receiving device needs to additionally include the process of forming the filters; this lengthens the process of fabricating the light receiving device and results in higher fabrication costs and lower yield of acceptable products.
One solution to the above problems is, as shown in FIG. 3, to use a wavelength separation mechanism 320 including a prism or a diffraction grating to separate the incident illumination light X into different single-color lights before it is shone to the light receiving section 310. In this case, however, the separated lights disperse and spread and thus illuminate a larger area; this results in a problem that it is impossible to downsize the light receiving section 310 (and hence the illumination light receiver 300).